Anemia is a condition of the blood characterized by a deficiency of erythrocytes (also known as red blood cells), hemoglobin, or total volume. Nearly 100 different types of anemia with a wide array of underlying causes and symptoms have been described.

Pernicious anemia is a form of the disease that is associated with an inability of the body to absorb vitamin B12. The name of the disease reflects the fact that it was often a fatal condition prior to the 1920s when the dietary nature of the condition was discovered and liver began to be utilized to treat it. The development of pernicious anemia is usually a gradual process that affects individuals 35 years of age or older. The disease may also begin in youth, but in such cases, usually appears before the age of 3. There appears to be a hereditary component involved in the development of pernicious anemia, an increased incidence for the disease being observed in some families.

If pernicious anemia is left untreated, irreparable neurological problems may develop that may become apparent as unsteadiness when walking, a tingling or a numb feeling in the hands and feet, irritability, memory loss, or severe personality changes that are sometimes referred to as megaloblastic madness. Few individuals incur such serious effects from pernicious anemia in modern times, although they were seen as inevitable steps on the path towards disease-related death in earlier periods. Today, treatment for pernicious anemia involves periodic intramuscular injections of vitamin B12. This form of therapy is very successful and usually provides rapid relief. The injections must be continued throughout life, however, or symptoms of pernicious anemia will return.

Vitamin B12 is a water-soluble, cobalt-containing vitamin essential to humans for the maturation of red blood cells. In individuals with pernicious anemia, however, vitamin B12 cannot be absorbed properly by the body because either the parietal cells of the stomach are unable to synthesize intrinsic factor, a substance that forms a complex with the vitamin in healthy individuals so that it is not degraded in the stomach and may be subsequently absorbed in the small intestine, or the intrinsic factor produced is hindered from binding with the vitamin. Such abnormalities, which prevent the proper synthesis of DNA because of insufficient vitamin B12 available, are generally assumed to arise from a malfunctioning of the autoimmune system. Without the normal ability to synthesize DNA, the nuclei of new red blood cells are never able to mature. The defective cells, known as megaloblasts, are usually obliterated by the bone marrow and, therefore, never enter into circulation. A small number of the cells, however, may develop into macrocytes, abnormally large red blood cells that are circulated in the blood but do not function in the normal way.

Pernicious Anemia at 20x Magnification - Pernicious anemia typically develops gradually and the initial signs of the disease, which may include weakness and fatigue, are vague. Other symptoms of pernicious anemia typically only occur in more severe case, but may include pallor, shortness of breath, rapid heart rate, anorexia, tongue soreness and redness, bleeding gums, and weight loss.